There have been many efforts to improve the quality of apparatus used for deep fat frying of various foods, both in fryers of a type to be used in a restaurant or the like and in the industrial cookers used for the continuous processing of large quantities of food. It is generally recognized that the oil needs to be maintained at the appropriate temperature to obtain the proper cooking, and it is well known that the immersion of a quantity of food into heated oil causes the temperature of the oil to go down. As a result, most of the prior art efforts to improve the cookers have taken the form of an improved heating means in an effort to put more heat into the oil to raise the temperature. There have also been efforts to distribute the heat properly so more heat is available where raw cold, perhaps frozen, product is put into the oil, and less heat is used after the product has been sufficiently heated so that less heat energy is required.
The prior art efforts at solving the problem of maintaining the desired oil temperature have not been successful largely because the improved heating means have taken the form of fire tubes or electrical heating elements that are raised to a very high temperature, but the heat cannot be transferred into the oil at a sufficiently high rate to achieve the overall desired cooking temperature. The result is that the oil reaches a low temperature when new product is placed into the oil, and the temperature increases rather gradually as heat is transferred, by conduction, from the heating means to the oil that is actually cooking the food.
The deep fat fryer conventionally used in restaurants and the like takes the form of a tank of oil having heating means in the tank, and a basket for holding the food to be lowered into the heated oil. Such an arrangement is highly undesirable from several standpoints, largely because of the lack of efficiency in using such an arrangement in a restaurant. In general, one basket can be used for only one food so the utilization of the fryer is minimal. A large fryer may have two baskets or more, but a separate basket is required for each separate food, and generally for each individual portion of each food. Additionally, such fryers suffer from the above discussed disadvantages of causing the oil to drop to a low temperature when the basket is dropped into the oil, then a high temperature heating element places heat into the oil, but only as fast as the heat can be transferred by conduction through the oil with some transfer by convection currents in the oil. One attempt at solving these problems is the use of an additional temperature sensing element to determine the temperature of the oil, and this sensing element provides the information to a computing device that calculates the amount of time necessary to cook the particular food at the temperature sensed. When the calculated time has elapsed, the computing device causes the basket to be lifted from the oil. Such a device is quite expensive, but does nothing towards solving the ultimate problem, which is the low temperature of the cooking oil at the point of cooking.
A further problem in the prior art fryers is the degradation of the oil. There have been efforts to keep fryers covered to prevent the surface oxidation of the oil in an effort to reduce the loss, and there has been some filtration of oil to remove the foreign matter and allow the oil to be used for longer periods. One of the greatest problems in the degradation of the oil, however, is the overheating of the oil. Due to the extremely high temperature surfaces used in an effort to place heat into the oil, great quantities of oil are degraded very rapidly. The temperature of these surfaces is frequently around 600.degree. F. to 1200.degree. F. (300.degree. C. to 650.degree. C.), and the rate of oil degradation doubles with each 20.degree. F. rise in temperature. As a result, it will be seen that the prior art effort at solving one problem has created another problem without really solving the first problem.
The prior art includes several forms of rotary drums used as conveyors in fryers and other food preparation devices. These prior art rotary drums have usually required loading in one specific location that would be unhandy in general use, especially in a restaurant or the like. Further, the unloading of the previous drums has been centrally of the drum, usually requiring an additional conveyor of the like. The unloading of the drum at a point that holds the cooked food over the hot oil is also undesirable since fried food has a very short acceptable life, and the vapor from the hot oil would degrade the product faster than a normal holding counter.